A high peak-white luminance is always required to achieve a good contrast ratio in every display technologies even with ambient light conditions and, for every kind of active displays, more peak white luminance corresponds to a higher power that flows in the electronic of the display. Therefore, if no specific management is done, the enhancement of the peak luminance for a given electronic efficacy will introduce an increase of the power consumption.
The main idea behind every kind of power management concept associated with peak white enhancement is based on the variation of the peak-luminance depending on the picture content in order to stabilize the power consumption to a specified value. This concept is shown in FIG. 1. When the picture load is low, the peak luminance is high and when the picture load is high, the peak luminance is low. The concept described on this figure enables to avoid any overloading of the power supply of the display panel as well as a maximum contrast for a given picture.
Such a concept suits very well to the human visual system. When the picture load is low, the contrast ratio is high and when the picture is high, the human eye is dazzled and is less sensitive to contrast ratio. So, for a full-white picture, the contrast ratio can be lower than for a peak-white picture.
In the case of cathode Ray Tubes (CRTs), the power management is based on a so called ABL function (Average Beam-current Limiter), which is implemented by analog means and which decreases video gain as a function of the average luminance of the pictures.
In the case of an organic light-emitting diode display, also called. OLED display, the luminance as well as the power consumption is directly linked to the current that flows through each cell. Currently, there is no power level control means for stabilizing the power consumption to a target value.
In the other hand, in such a display device, the contrast is adjusted by a video scaler acting on the video signal. If the video signal is coded on 8 bits and if the contrast should be reduced by 50%, the video signal is rescaled leading to a video signal with only a 7 bit resolution. So, there is a loss of video resolution.